It is known that for sweeping glass surfaces, especially windshields of motor vehicles, windshield wipers which are driven in a regular oscillating sweeping movement are employed. In general, such a wiper comprises a windshield wiper arm which is moved in an oscillating rotational movement and which is articulated to a wiper blade. Again, such a wiper blade conventionally includes a main carrier element, typically in the form of a yoke, having means for coupling it with the windshield wiper arm. A flexible wiping strip, typically of rubber, is supported by the main carrier element, and the wiping strip engages the swept surface.
With a view to obtaining maximum effectiveness in operation over the entire length of the wiping strip, it is necessary to try to ensure that the wiping strip is applied against the swept surface with a pressure which is an uniform as possible over its length. In known types of windshield wiper blades, a wiping strip is retained by means of a plurality of yokes which are articulated on the main support yoke. Each of these further yokes is so arranged as to enable two attachment points for the wiping strip to be disposed in such a way as to give the best possible distribution of the pressure applied on the swept surface by the wiping strip, in relation to the position of the point at which the relevant yoke is articulated in the support structure of the blade.
The disadvantage of such blades lies in the fact that windshields are curved, in particular towards side edges thereof, so that the distribution of the application force tends to lead to loss of contact between the wiping strip and the swept surface, especially towards the extreme outer end of the blade.
French published patent application No. FR 1 145 640A discloses a wiper blade comprising a main carrier element, at one of the ends of which is articulated a pressure lever. The free end of this pressure lever is engaged in a sliding manner with the outer free end of the wiping strip, and the pressure lever is under the influence of a spring such that it can pivot about the articulation point towards the swept surface, thus enabling the wiping strip to be able to hug the curvature of the swept surface.
Such wiper blades have however been found to have a number of drawbacks. In particular, it has proved necessary to provide a specially designed main carrier element which comprises a number of components for receiving the pressure lever, thus rendering the supporting structure for the wiping strip more complicated and increasing the cost of the blade itself.
In addition, when the pressure lever is subjected to a rotational force around its axis towards the swept surface, the attachment point of the pressure lever on the wiping strip undergoes sliding movement, such that it moves further away from the extreme longitudinal region of the wiping strip. This movement leads to loss of contact in this region between the wiping strip and the swept surface. When the vehicle is in motion and the windshield wiper is parked, this loss of contact sets up vibration at that end of the wiper blade, which is uncomfortable for the occupants of the vehicle and which can also lead to loss of performance of the wiping strip.